The Role of Context in Sleep-related Memory Reactivation in Humans: Reactivating Specific Memories During Sleep in Conjunction with a Suppression Context

Each participant will be run in a single afternoon, which includes a 90-minute nap opportunity. Before the nap, participants will go through training and test sessions - and after it they will partake of final memory tests. Neural activity will be continuously monitored and recorded throughout the task using electrophysiological equipment. Breathing activity will also be measured.

This is a within-subjects study. The main manipulation is the unobtrusive presentation of sounds and odors during sleep, a technique called targeted memory reactivation (TMR). All participants will experience these stimuli, including all three odors, but the specific sounds each participant will hear will be different. Additionally, each of the three odors will be associated with specific instructions during wake (i.e., one odor instructing to remember a preceding word, another to forget it and one odor which will not be associated with any instructions). Odors will be counterbalanced across participants. The results will then be compared within participant, not between different groups or individuals. Appropriate statistical methods for such analyses include paired t-test and repeated measures analysis of variance. The choice of which sounds will be presented in conjunction with each of the odors (and which will not presented at all) for each participant will be made based on their performance in the pre-sleep test. This will be done in an attempt to balance pre-sleep scores between presented and unpresented stimuli to remove statistical noise. Both the participant and the experimenter will be blind to which sounds will be presented when, and the selection will be automatically made by the computer. This technique has been extensively used and has no known risks.

There are two main reasons that using a within-subject design reduces the required sample size. First, the lack of a between-subject independent variable intuitively requires less participants. Second, the level of statistical noise due to individual differences is reduced (i.e., because each participant is compared with their own scores). Previous TMR studies, which have found significant cuing effects, commonly used 20-25 participants. I plan to include at least 30 participants in this study, after omitting participants who could not complete the task and those who were not sufficiently cued during sleep. Having 30 participants will allow the use of more powerful statistical methods (in accordance with the common rule of thumb derived from the central limit theorem, which states that means based on sample sizes of more than 30 participants can be assumed to follow a normal distribution). My main interest in this study is the suppression TMR effect. It is hard to estimate the effect size of this detrimental effect, but it may be somewhat smaller than the typical TMR effect for spatial learning memories (Hedge's g = 0.39 based on a recent meta-analysis). To be on the safe side, I included a higher sample size. It is important to note that even if this benefit will be of a smaller magnitude, it will still be indicative of the potential for weakening memories during sleep. Aiming at a sample size of at least 30 participants and assuming an omission rate of 80%, I therefore plan to have 38 participants altogether.

Here is a brief summary of the procedure:

Stimuli: Three distinct odors which are equally arousing and pleasant will be used, for this study. A set of 100 nouns will be used to train participants on the directed forgetting task (see below). Finally, 60 images of objects or animals will be used, each with a unique 2D position on a circular grid presented on the screen.